A restaurateur who lost out on the concession to run the Loeb Boathouse in Central Park — even though his offer was $19.5 million higher than the winner — is now suing the city, charging that he lost out to a bidder who should never have been involved in the process because he donated to Mayor Bill de Blasio’s Campaign for One New York.

Robert Towers, who once ran the Bryant Park Grill, is suing the city to void the contract awarded to longtime Loeb Boathouse operator Dean Poll.

The lakeside restaurant is among the city’s most popular wedding venues.

Towers says in his Manhattan civil suit that Poll should have been disqualified from bidding for the 15-year concession, largely because he donated $10,000 to the mayor’s nonprofit, which is now shuttering amid an ethics probe, in what the state Board of Elections called a potential conflict of interest.

The Post could not find a record of Poll donating to

The Campaign for One New York, but he did give $10,000 to the New York State Democratic Campaign Committee in October 2014. The State Board of Elections said in a January document that Poll’s donation to the committee may be a conflict of interest because it was made at the mayor’s behest while Poll had business before the city.

Under city laws Poll “would not have been permitted to contribute more than $400…to the mayor directly,” according to the Board of Elections.

“Dean Poll’s donation to Mayor de Blasio’s Campaign for One New York can be characterized as one made to ‘pay-to-play’ to” continue running the Central Park landmark.

Towers’ attorney, Lawerence Goldberg, acknowledged that the donation may have been made to the Democratic Campaign Committee and not the mayor’s nonprofit but said it was a “distinction without a difference” because the intent was the same– to turn around the state senate and support de Blasio’s agenda.

The mayor was silent on Poll’s bid even though in 2011 as public advocate, he said the city shouldn’t be doing business with the restaurateur because of sexual harassment complaints by former employees.

Poll’s hiring of James F. Capalino Associates, a lobbying firm linked to de Blasio, coincided with the bid renewal process in late 2015 and early 2016, the suit says. That retention was prohibited by state law because Poll had a pending bid before the city at the time, according to court papers.

The Parks Department used “changed selection criteria” that “benefitted only Dean Poll” by downplaying his history of labor violations and underreported revenue.

Awarding the lucrative boathouse concession to Poll is illegal because it was based on “unfair dealing,” the suit says.

“As a matter of law competitive bidding serves to prevent favoritism, improvidence, fraud and corruption in the awarding of public contracts,” the suit says.

The Parks Department told Towers that Poll was the winning bidder even though Poll only offered a minimum $19.2 million in fees over 15 years to the city while Towers proposed $38.8 million.

The new concession starts in December.

A city spokesman said the Parks Department “conducted a competitive and fair selection process for the Loeb Boathouse concessionaire, strictly adhering to the City’s Franchise and Concession Review Committee Rules.”

Poll told The Post he didn’t recall the $10,000 donation because he gives a lot of money to different politicians and groups. He said he didn’t think a $10,000 contribution to the mayor’s nonprofit or the committee would constitute a conflict of interest. He also doesn’t believe that he violated any rules hiring the lobbyist.

He called Towers’ higher bid a “pie in the sky” offer while his figure is based on “real numbers.”